The study of the characterization of alterations in membrane structural components of lymphocytes with senescence requires an understanding of lymphocytic responses in immunogenic interactions, which decrease with age. The project is concerned with the quantitative aspect of in vitro activated T lymphocytes. The assay involves the infection of activated lymphocytes with vesicular stomatitis virus (VSV) and the subsequent plating of infected cells on T cell monolayers for determination of virus plaque-forming cells (V-PFC). The effect of interferon, a byproduct of T cell activation on the V-PFC assay, is examined. In addition, the interferon, as well as the initial number of T lymphocytes responding to a stimulation, is compared between different mouse strains.